The present invention is directed to the production of desensitized and storage stable, aliphatic diperoxyalkanedioic acids, and aromatic peroxycarboxylic acids.
Solid, water insoluble, peroxycarboxylic acids showed thermal and mechanical sensitivity when in the pure or highly concentrated condition. Various methods are described in the literature for the safe handling of these compounds (D. Swern Organic Peroxides Vols. I, II and III, 1970-1972: R. Criegee in Houben--Weyl Vol. 8). Methods of preparing diperoxyalkanedioic acids are disclosed in Swern, Organic Peroxides Vol. I, pages 388-392 and the references cited therein as well as McCune, Canadian Pat. No. 635,620. Methods of preparing aromatic peroxycarboxylic acids are disclosed in German application No. P 29 29 839.3, July 23, 1979.
A desensitization can also be provided under certain conditions by the addition of alkali, alkaline earth, aluminium and ammonium salts of strong mineral acids as, e.g. sulfuric acid.
Thereby there have already been attempts to further lower the tendency to decomposition or spontaneous decomposition by using salts which were low in water of hydration in order that the thus stabilized peroxycarboxylic acids could take up moisture occuring in storage, see Belgian Pat. No. 560,389. Conversely it has also already been proposed to reduce the tendency to decomposition through such of the above mentioned salts which form hydrates and by mixing them in their hydrate form, see German Pat. No. 1,468,847.
According to the process of German AS No. 1,668,569 and German Pat. No. 1,668,570 it was proposed to feed peroxycarboxylic acids dispersed in water into a fluidized bed of a salt hydrate. Thereby the particles of the percarboxylic acids should be coated with a jacket of the hydrate. However, there are placed quite specific requirements on the hydrate in reference to the temperatures at which the water of crystallization is first permitted to be given up or there can only be employed very specific hydrates.
The jackets built thereby, however, were not without flaws, entirely apart from the fact that the process was very expensive and the mixture were inclined to cake together.
Therefore in recent times there has again been a return to the simple mixture of the dry acid or water wet acid with the dry salts.
However, a sure desensitization can only occur if there is present a homogeneous and dilute mixture.
In a process such as that described for example in McCune Canadian Pat. No. 635,620 and Gougeon German OS No. 2,422,691 and Gougeon German OS No. 2,422,735, the desensitizing agent is mixed in subsequently. As a result of this, there is the danger of a partial inhomogeneity. A further disadvantage is that the dry mixing of a high percentage of peroxy acid with the desensitizing agent under some circumstances leads to a higher mechanical sensitivity which is produced by the shearing effects on the edges of the crystals.